Modified nickel-based positive electrode material, preparation method thereof and lithium ion battery

Abstract

A modified nickel-based positive electrode material comprises a nickel-based positive electrode material matrix and a doping element doped in the nickel-based positive electrode material matrix, the electronegativity of the doping element is higher than that of lithium and transition metal elements in the nickel-based positive electrode material matrix, and the porosity of the material is 10%-20%. The preparation method comprises the following steps: mixing and sintering a positive electrode material precursor, a lithium source and a doping agent to obtain a sintered product; washing and drying the sintered product to obtain a washed product; and mixing the washed product with a coating agent, and sintering to obtain the modified nickel-based positive electrode material. The invention also discloses a lithium ion battery. In the modified nickel-based positive electrode material, a part of doped elements enter a lattice body of a nickel-based positive electrode material matrix, the electronegativity of the doped elements is larger than that of lithium and transition metal elements, the doped elements have higher covalence, higher bond strength and higher oxidation potential, lattice oxygen in the structure is stabilized, precipitation of the lattice oxygen is reduced, and therefore the structural stability of the material is improved.

Description

Technical Field

[0001] The present invention belongs to the field of lithium-ion batteries, and particularly relates to an intercalation pore-forming modified nickel-based cathode material, a preparation method thereof, and a lithium-ion battery. Background Art

[0002] In order to meet the increasing demand for driving range in the new energy vehicle market, the competition for high-energy density batteries has increased, and high-energy lithium-ion batteries have been greatly developed. In the race for energy density, it is particularly urgent to develop lithium-ion battery materials with higher energy density and cycle life. Nickel-based cathode materials have received extensive attention due to their characteristics of high capacity and high voltage platform.

[0003] The development of nickel-based cathode materials tends to be high-nickel and high-voltage. Increasing the nickel content and working voltage is the most direct way to improve the specific capacity, but at the same time, there are also problems such as high residual lithium, unstable bulk structure, serious lithium-nickel mixing, surface side reactions, long lithium-ion transmission distance, and poor ionic conductivity, which have an impact on capacity, rate, and long-term cycle performance. At present, in the existing technologies, doping and coating and other modification means are used to solve the above problems, but the doping modification effect is still poor, and problems such as unstable bulk structure, surface side reactions, long lithium-ion transmission distance, and poor ionic conductivity still exist, affecting the electrochemical performance of nickel-based cathode materials. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the above-mentioned deficiencies and defects in the background art, and provide a modified nickel-based cathode material, a preparation method thereof, and a lithium-ion battery.

[0005] To solve the above technical problem, the technical solution proposed by the present invention is as follows:

[0006] A modified nickel-based cathode material includes a nickel-based cathode material matrix and a doping element doped in the nickel-based cathode material matrix. The doping element includes a doping element L with high electronegativity, and the electronegativity of the doping element L is higher than that of lithium and transition metal elements in the nickel-based cathode material matrix. The porosity of the modified nickel-based cathode material is 10%-20%.

[0007] The electronegativity of the doping element L is greater than that of lithium and transition metal elements in the nickel-based cathode material matrix, has stronger covalency, higher bond strength, higher oxidation potential, stabilizes the lattice oxygen in the structure, reduces the precipitation of lattice oxygen, and thus improves the structural stability of the material. A part of the doping element L enters the lattice of the nickel-based cathode material matrix, and the other part adheres to the gaps between primary particles inside the matrix to form an intercalation structure. The intercalated substance existing in the gaps between primary particles is removed by a specific water washing process to achieve the effect of pore formation and form a material with high porosity.

[0008] For the above-mentioned modified nickel-based cathode material, preferably, the electronegativity value of the doping element L > 2.0.

[0009] For the above-mentioned modified nickel-based cathode material, preferably, the doping element L includes at least one of B, C, N, S, F, Cl, Br, or I.

[0010] For the above-mentioned modified nickel-based cathode material, preferably, the mass of the doping element L accounts for 0.05% - 0.2% of the mass of the modified nickel-based cathode material.

[0011] For the above-mentioned modified nickel-based cathode material, preferably, the specific surface area of the modified nickel-based cathode material is 0.8 - 1.5 m 2 / g, and the total residual lithium on its surface is 1000 - 1800 ppm.

[0012] For the above-mentioned modified nickel-based cathode material, preferably, the chemical general formula of the modified nickel-based cathode material is Li z Ni 1-x-y Co x Me y L u M v N w O 2-t , where 0.9 ≤ z ≤ 1.1, 0 ≤ x ≤ 0.2, 0 ≤ y ≤ 0.2, 0 < u ≤ 0.007, 0 ≤ v ≤ 0.01, 0 ≤ w ≤ 0.01, -0.05 ≤ t ≤ 0.05, Me is at least one of Mn and Al, M is at least one of Na, K, Mg, Ca, Sr, Ba, Zr, Ti, and Y, and N is at least one of B, La, Ce, Al, Co, Ti, or W.

[0013] As a general inventive concept, the present invention also provides a preparation method of the above-mentioned modified nickel-based cathode material, including the following steps:

[0014] (1) Mix the cathode material precursor, lithium source, and dopant evenly and then perform sintering treatment to obtain a sintered product;

[0015] (2) Wash and dry the sintered product obtained in step (1) to obtain a washed product;

[0016] (3) Mix the washed product obtained in step (2) evenly with a coating agent containing element N, and then perform sintering treatment to obtain the modified nickel-based cathode material.

[0017] In the preparation method of the present invention, a part of element L enters the lattice of the nickel-based cathode material matrix, and the other part adheres to the gaps between the primary particles inside the matrix, forming an intercalation structure. The intercalation substances existing in the gaps between the primary particles can be removed through a specific water washing process, achieving the effect of pore formation and forming a modified nickel-based cathode material with high porosity.

[0018] In the above preparation method, preferably, in step (1), the dopant is a dopant containing element L, and the mass ratio of its addition amount to the mass of the cathode material precursor is denoted as a, where a is 2% - 8%. By matching a high addition amount of an intercalation compound containing dopant element L with a specific water washing process, the present invention can form a material with high porosity, which can shorten the diffusion distance of lithium ions, increase the diffusion rate of lithium ions, exhibit a higher capacity, and improve the rate performance of the material at the same time.

[0019] In the above preparation method, preferably, in step (1), the dopant containing element L is an inorganic acid salt, and its solubility s at 20°C is greater than 10 g / 100 g of water.

[0020] In the above preparation method, preferably, in step (2), during the water washing process, the solid-liquid mass ratio is denoted as b, and b ≤ s(1 + a) / 500a, ensuring that the intercalation substances in the gaps between the primary particles inside the matrix can be removed during the water washing process, thereby achieving the purpose of pore formation.

[0021] In the above preparation method, preferably, in step (2), during the water washing process, the solid-liquid mass ratio b is 0.5 - 1.8, the water washing temperature is 5 - 25°C, and the stirring speed is 500 - 900 rpm.

[0022] In the above preparation method, preferably, in step (1), the sintering treatment includes two-stage sintering. The sintering temperature of the first stage is 400 - 600°C, and the heat preservation time is 2 - 5 h. The sintering temperature of the second stage is 700 - 900°C, and the heat preservation time is 8 - 20 h.

[0023] In the above preparation method, preferably, in step (3), the sintering temperature of the sintering treatment is 300 - 700°C, and the sintering heat preservation time is 4 - 10 h.

[0024] In the above preparation method, preferably, the lithium source is at least one of lithium carbonate, lithium hydroxide, lithium nitrate, and lithium phosphate.

[0025] In the above preparation method, preferably, the dopant is an inorganic acid salt containing both elements M and L.

[0026] As a general inventive concept, the present invention also provides a lithium-ion battery, and the positive electrode material used in the lithium-ion battery is the above-mentioned modified nickel-based positive electrode material or the modified nickel-based positive electrode material obtained by the above-mentioned preparation method.

[0027] Compared with the prior art, the advantages of the present invention are as follows:

[0028] (1) For the modified nickel-based positive electrode material of the present invention, the nickel-based positive electrode material is doped and modified with a highly electronegative doping element L. A part of the doping element L enters the lattice of the nickel-based positive electrode material matrix. Its electronegativity is greater than that of lithium and transition metal elements in the material matrix, with stronger covalency, higher bond strength, higher oxidation potential, stabilizing the lattice oxygen in the structure, reducing the precipitation of lattice oxygen, and thus improving the structural stability of the material.

[0029] (2) For the modified nickel-based positive electrode material of the present invention, the nickel-based positive electrode material is doped and modified with a highly electronegative doping element L. Another part of the doping element L adheres to the gaps between primary particles inside the matrix, inhibits the growth of primary particles, forms an intercalation structure, and the intercalation substances existing in the gaps between primary particles are removed by a subsequent specific water washing process to achieve the effect of pore formation, forming a material with high porosity, reducing the diffusion distance of lithium ions, and thus exerting a higher capacity.

[0030] (3) When preparing the modified nickel-based positive electrode material by the preparation method of the present invention, in addition to washing away the highly soluble intercalation substances from the matrix by a specific water washing process to achieve the pore formation function and form a matrix of a material with high porosity, the residual alkali on the surface of the material matrix can also be washed away at the same time to form a low-impedance surface layer, shorten the diffusion distance of lithium ions, increase the diffusion rate of lithium ions, exert a higher capacity, and improve the rate performance of the material.

[0031] (4) The preparation method of the present invention adopts a surface coating and dry sintering process to repair the surface structure defects generated during the water washing process of the high-nickel material, reduce the surface stress of the material, and at the same time can react with the residual lithium on the surface to further reduce the residual lithium, and reduce the specific surface area of the material to form an ion conductor layer to protect the surface of the material, reduce the side reaction with the electrolyte during the cycle, and improve the cycle stability of the material; it can also fix the oxygen atoms on the surface while establishing a lithium ion transmission channel, inhibit the generation of the side reaction nickel oxide phase of the high-nickel component on the surface of the high-nickel material during the cycle, and improve the cycle stability of the material. Description of the Drawings

[0032] Figure 1 is the SEM image of the sintered product obtained in step (1) of Example 1 of the present invention;

[0033] Figure 2 is the SEM image of the water-washed product obtained in step (2) of Example 1 of the present invention;

[0034] Figure 3 It is the SEM image of the modified nickel-based cathode material prepared in Example 1 of the present invention;

[0035] Figure 4 It is the sectional view of the modified nickel-based cathode material prepared in Example 1 of the present invention;

[0036] Figure 5 It is the SEM image of the modified nickel-based cathode material prepared in Comparative Example 1 of the present invention;

[0037] Figure 6 It is the sectional view of the modified nickel-based cathode material prepared in Comparative Example 1 of the present invention. Detailed implementation manners

[0038] For the convenience of understanding the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with the accompanying drawings of the specification and preferred embodiments, but the protection scope of the present invention is not limited to the following specific embodiments.

[0039] Unless otherwise defined, all the technical terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention.

[0040] Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment, etc. used in the present invention can be obtained through the market or can be prepared by existing methods.

[0041] Example 1:

[0042] A modified nickel-based cathode material of the present invention includes a nickel-based cathode material matrix and a doping element doped in the nickel-based cathode material matrix, and its chemical formula is Li 1.0 Ni 0.900 Co 0.045 Mn 0.055 S 0.0056 B 0.001 O 1.9944 , where S is the doping element and B is the coating element. This modified nickel-based cathode material consists of secondary spherical polycrystals, the particle size D50 is 9.83 μm, the specific surface area is 1.04 m 2 / g, the total residual lithium is 1418 ppm, the porosity of this modified nickel-based cathode material is 12.21%, and the mass of the doping element S accounts for 0.17% of the total mass of the modified nickel-based cathode material.

[0043] The preparation method of the modified nickel-based cathode material in this example includes the following steps:

[0044] (1) Mix the nickel-cobalt-manganese hydroxide precursor Ni 0.90 Co0.045 Mn 0.055 (OH)2, lithium hydroxide monohydrate, and lithium sulfate were added to a high-speed mixing stirrer in a molar ratio of 1:1.05:0.03, stirred at a speed of 1800 r / min for 30 min, then in a box furnace with an oxygen concentration ≥ 96%, heated at a rate of 3 °C / min to 500 °C and held for 2 h, then heated to 754 °C and held for 11 h, naturally cooled to room temperature, pulverized, and passed through a 300-mesh sieve to obtain a sintered product; the SEM image of the sintered product is as shown in Figure 1 shown. It can be seen from the figure that the material consists of secondary spherical crystals composed of primary particles, and lithium sulfate is inserted into the gaps between the primary particles in the form of flakes, presenting an intercalated structure;

[0045] (2) According to the mass ratio a of the dopant lithium sulfate to the nickel-cobalt-manganese hydroxide precursor being 5.6% and the solubility s of the dopant being 25 g / 100 g of water, it is calculated that the solid-liquid mass ratio during the water washing process should be less than 0.94. Then, the sintered product was washed with deionized water, controlling the solid-liquid mass ratio b of the washing to be 0.9, the temperature of the deionized water to be 8 °C, and the stirring speed to be 700 rpm, washed for 10 min. After water washing, the sample was placed in a vacuum oven and vacuum dried at 140 °C for 6 h, then naturally cooled to room temperature and passed through a 300-mesh sieve to obtain a water-washed product; the electron microscope image of the water-washed product is as shown in Figure 2 shown. The flaky lithium sulfate in the matrix disappeared and was washed away by dissolving in water;

[0046] (3) The water-washed product and boric acid were added to a high-speed mixing stirrer in a molar ratio of 1:0.001, stirred at a speed of 1800 r / min for 30 min, then in a box furnace under an oxygen atmosphere, heated at a rate of 3 °C / min to 300 °C and held for 6 h, naturally cooled to room temperature, and screened using a 300-mesh sieve to obtain the modified nickel-based cathode material of this example. Its electron microscope image is as shown in Figure 3 shown, and the cross-sectional view is as shown in Figure 4 shown. It can be seen from the figure that the material has a relatively large porosity, and there are uniform pores between the primary particles. Through image processing calculation, its porosity is 12.21%.

[0047] Example 2:

[0048] A modified nickel-based cathode material of the present invention includes a nickel-based cathode material matrix and a doping element doped in the nickel-based cathode material matrix, and its chemical formula is Li 0.9956 Na 0.0044 Ni 0.900 Co 0.045 Mn 0.055 Cl 0.0044 B 0.001 O 1.9956, where Na and Cl are doping elements, and B is a coating element. The modified nickel-based cathode material consists of secondary spherical polycrystals, with a particle D50 size of 9.73 μm, a specific surface area of 0.94 m 2 / g, a total residual lithium of 1258 ppm, a porosity of 15.99% for the modified nickel-based cathode material, and the mass of doping element Cl accounts for 0.15% of the total mass of the modified nickel-based cathode material.

[0049] The preparation method of the modified nickel-based cathode material of this embodiment includes the following steps:

[0050] (1) Add nickel-cobalt-manganese hydroxide precursor Ni 0.90 Co 0.045 Mn 0.055 (OH)2, lithium hydroxide monohydrate, and sodium chloride into a high-speed mixing blender according to a molar ratio of 1:1.05:0.03, stir at a speed of 1800 r / min for 30 min, then in a box furnace with an oxygen concentration ≥ 96%, heat up at a rate of 3 °C / min to 500 °C and hold for 2 h, then heat up to 754 °C and hold for 11 h, naturally cool to room temperature, crush, and pass through a 300-mesh sieve to obtain a sintered product;

[0051] (2) According to the mass ratio a of dopant sodium chloride to nickel-cobalt-manganese hydroxide precursor being 3.0% and the solubility s of the dopant being 36 g / 100 g of water, calculate that the solid-liquid mass ratio in the water washing process should be less than 2.4, then wash the sintered product with deionized water, control the solid-liquid mass ratio b = 1.0 in the washing process, the temperature of the deionized water is 8 °C, the stirring speed is 700 rpm, wash for 10 min, after water washing, place the sample in a vacuum oven, vacuum dry at 140 °C for 6 h, then naturally cool to room temperature, and pass through a 300-mesh sieve to obtain a water-washed product;

[0052] (3) Add the water-washed product and boric acid into a high-speed mixing blender according to a molar ratio of 1:0.001, stir at a speed of 1800 r / min for 30 min, then in a box furnace under an oxygen atmosphere, heat up at a rate of 3 °C / min to 300 °C and hold for 6 h, naturally cool to room temperature, and sieve using a 300-mesh sieve to obtain the modified nickel-based cathode material of this embodiment.

[0053] Example 3:

[0054] A modified nickel-based cathode material of the present invention includes a nickel-based cathode material matrix and doping elements doped in the nickel-based cathode material matrix, and its chemical formula is Li 0.9957 K 0.0043 Ni 0.900 Co 0.045 Mn 0.055 F 0.0043 B 0.001 O1.9957 , where K and F are doping elements, and B is a coating element. The modified nickel-based cathode material consists of secondary spherical polycrystals, with a particle D50 size of 9.78 μm, a specific surface area of 0.94 m 2 / g, a total residual lithium of 1304 ppm, a porosity of 17.82% for the modified nickel-based cathode material, and the mass of doping element F accounts for 0.08% of the total mass of the nickel-based cathode material.

[0055] The preparation method of the modified nickel-based cathode material of this example includes the following steps:

[0056] (1) Add nickel-cobalt-manganese hydroxide precursor Ni 0.90 Co 0.045 Mn 0.055 (OH)2, lithium hydroxide monohydrate, and potassium fluoride into a high-speed mixing blender according to a molar ratio of 1:1.05:0.03, stir at a speed of 1800 r / min for 30 min, then in a box furnace with an oxygen concentration ≥ 96%, heat up at a heating rate of 3 °C / min to 500 °C and hold for 2 h, then heat up to 754 °C and hold for 11 h, naturally cool to room temperature, crush, and pass through a 300-mesh sieve to obtain a sintered product;

[0057] (2) According to the mass ratio a of dopant potassium fluoride to nickel-cobalt-manganese hydroxide precursor being 2.9% and the solubility s of the dopant being 95 g / 100 g of water, calculate that the solid-liquid mass ratio during the water washing process should be less than 6.52. Then wash the sintered product with deionized water, control the solid-liquid mass ratio b of the washing to be 1.0, the temperature of the deionized water to be 8 °C, the stirring speed to be 700 rpm, wash for 10 min, place the sample in a vacuum oven after water washing, vacuum dry at 140 °C for 6 h, then naturally cool to room temperature, and pass through a 300-mesh sieve to obtain a water-washed product;

[0058] (3) Add the water-washed product and boric acid into a high-speed mixing blender according to a molar ratio of 1:0.001, stir at a speed of 1800 r / min for 30 min, then in a box furnace under an oxygen atmosphere, heat up at a heating rate of 3 °C / min to 300 °C and hold for 6 h, naturally cool to room temperature, and screen using a 300-mesh sieve to obtain the modified nickel-based cathode material of this example.

[0059] Comparative Example 1:

[0060] The modified nickel-based cathode material of this comparative example has the chemical formula Li 1.0 Ni 0.90 Co 0.045 Mn 0.055 B 0.001 O2, consists of secondary spherical polycrystals, with a particle D50 size of 9.8 μm, a specific surface area of 0.48 m 2 / g, the total residual lithium is 1150 ppm, and the porosity of the nickel-based cathode material is 1.2%.

[0061] The preparation method of the modified nickel-based cathode material in this comparative example is only different from that in Example 1 in that no lithium sulfate dopant is introduced. The preparation steps are as follows:

[0062] (1) Add nickel-cobalt-manganese hydroxide precursor Ni 0.90 Co 0.045 Mn 0.055 (OH)2 and lithium hydroxide monohydrate into a high-speed mixing blender according to a molar ratio of 1:1.05, stir at a speed of 1800 r / min for 30 min, and then in a box furnace with an oxygen concentration ≥ 96%, heat up to 500 °C at a heating rate of 3 °C / min and hold for 2 h, then heat up to 754 °C and hold for 11 h, naturally cool to room temperature, pulverize, and pass through a 300-mesh sieve to obtain the primary sintered material;

[0063] (2) Wash the primary sintered material with deionized water. The solid-liquid mass ratio of the washing is 1.0, the temperature of the deionized water is controlled at 8 °C, the stirring speed is 700 rpm, wash for 10 min, after washing, place the sample in a vacuum oven, vacuum dry at 140 °C for 6 h, then naturally cool to room temperature, and pass through a 300-mesh sieve to obtain the washed material;

[0064] (3) Add the washed material and boric acid into a high-speed mixing blender according to a molar ratio of 1:0.001, stir at a speed of 1800 r / min for 30 min, and then in a box furnace under an oxygen atmosphere, heat up to 300 °C at a heating rate of 3 °C / min and hold for 6 h, naturally cool to room temperature, and screen with a 300-mesh sieve to obtain the modified nickel-based cathode material.

[0065] The SEM image of the modified nickel-based cathode material in this comparative example is as Figure 5 shown. It can be seen from the figure that the material is composed of secondary spherical crystals composed of primary particles, and its cross-sectional view is as Figure 6 shown. It can be seen from the figure that the overall porosity of the matrix material is small. Through image processing calculation, its porosity is 1.2%. Comparing with Example 1, the internal porosity of the matrix in this comparative example is small, and the capacity, rate and cycle performance are generally poor.

[0066] Comparative Example 2:

[0067] The modified nickel-based cathode material in this comparative example has the chemical formula Li 1.0 Ni 0.90 Co 0.045 Mn 0.055 S 0.0012 B 0.001 O 0.99 88, its nickel-based cathode material is composed of secondary spherical polycrystals, with a particle D50 particle size of 9.83 μm, a specific surface area of 0.70 m 2 / g, the total residual lithium is 1432 ppm, the porosity of the nickel-based cathode material is 2.16%, and the mass of the doped element S accounts for 0.03% of the total mass of the modified nickel-based cathode material.

[0068] The preparation method of the modified nickel-based cathode material in this comparative example includes the following steps:

[0069] (1) Add nickel-cobalt-manganese hydroxide precursor Ni 0.90 Co 0.045 Mn 0.055 (OH)2, lithium monohydrate hydroxide, and lithium sulfate into a high-speed mixing blender according to a molar ratio of 1:1.05:0.005, stir at a speed of 1800 r / min for 30 min, and then in a box furnace with an oxygen concentration ≥ 96%, heat up to 500 °C at a heating rate of 3 °C / min and hold for 2 h, then heat up to 754 °C and hold for 11 h, naturally cool to room temperature, crush, and pass through a 300-mesh sieve to obtain a primary sintered material;

[0070] (2) Wash the primary sintered material with deionized water, with a solid-liquid mass ratio of 1.0 for washing, control the temperature of the deionized water at 8 °C, stir at a speed of 700 rpm for 10 min, place the sample in a vacuum oven after washing, vacuum dry at 140 °C for 6 h, then naturally cool to room temperature, and pass through a 300-mesh sieve to obtain the washed material;

[0071] (3) Add the washed material and boric acid into a high-speed mixing blender according to a molar ratio of 1:0.001, stir at a speed of 1800 r / min for 30 min, then in a box furnace under an oxygen atmosphere, heat up to 300 °C at a heating rate of 3 °C / min and hold for 6 h, naturally cool to room temperature, and screen with a 300-mesh sieve to obtain the modified nickel-based cathode material.

[0072] Comparative Example 3:

[0073] The nickel-based cathode material in this comparative example has the chemical formula Li 1.0 Ni 0.89 Co 0.045 Mn 0.055 S 0.014 B 0.001 O 0.986 , its nickel-based cathode material is composed of secondary spherical polycrystals, with a particle D50 particle size of 9.94 μm, a specific surface area of 0.51 m 2 / g, the total residual lithium is 2227 ppm, the porosity of the nickel-based cathode material is 3.83%, and the mass of the doped element S accounts for 0.45% of the total mass of the nickel-based cathode material.

[0074] The preparation method of the modified nickel-based cathode material of this comparative example includes the following steps:

[0075] (1) Add nickel-cobalt-manganese hydroxide precursor Ni 0.90 Co 0.045 Mn 0.055 (OH)2, lithium hydroxide monohydrate, and lithium sulfate into a high-speed mixing blender according to a molar ratio of 1:1.05:0.03, stir at a rotation speed of 1800 r / min for 30 min, then in a box furnace with an oxygen concentration ≥ 96%, heat up at a heating rate of 3 °C / min to 500 °C and hold for 2 h, then heat up to 754 °C and hold for 11 h, naturally cool to room temperature, pulverize, and pass through a 300-mesh sieve to obtain the primary sintered material;

[0076] (2) Wash the primary sintered material with deionized water. The solid-liquid mass ratio of the washing is 3.0, the temperature of the deionized water is controlled at 8 °C, the stirring rotation speed is 700 rpm, wash for 10 min, after washing, place the sample in a vacuum oven, vacuum dry at 140 °C for 6 h, then naturally cool to room temperature, and pass through a 300-mesh sieve to obtain the material after washing;

[0077] (3) Add the material after washing and boric acid into a high-speed mixing blender according to a molar ratio of 1:0.001, stir at a rotation speed of 1800 r / min for 30 min, then in a box furnace under an oxygen atmosphere, heat up at a heating rate of 3 °C / min to 300 °C and hold for 6 h, naturally cool to room temperature, and screen with a 300-mesh sieve to obtain the modified nickel-based cathode material.

[0078] Performance test:

[0079] Use CR2032 coin cells to study the electrochemical performance of the cathode materials in the above examples and comparative examples.

[0080] Positive electrode sheet: Stir and disperse the cathode materials of Examples 1-3 and Comparative Examples 1-3, conductive carbon black (SP), and polyvinylidene fluoride (PVDF) in a mass ratio of 92.5:5:2.5 with the solvent NMP, coat it on an aluminum foil substrate, and roll it to obtain the positive electrode sheet.

[0081] Negative electrode sheet: Lithium metal sheet.

[0082] Electrolyte: 1 mol / L LiPF6 solution, the solvent is a mixed solvent of EC and DMC, the ratio of the two is 1:2, and the additive is 1% VC.

[0083] Assemble into CR2032 coin cells for battery testing. The charging cut-off voltage is 4.35 V, the discharging cut-off voltage is 3.0 V, and the test results of the electrical performance are shown in Table 1.

[0084] Table 1: Electrochemical Performance Test Results of Cathode Materials in Examples 1-3 and Comparative Examples 1-3

[0085]

[0086] As can be seen from Table 1, the modified nickel-based cathode materials in Examples 1-3 can significantly improve the initial discharge capacity and rate performance of the materials, and can significantly improve the high-temperature cycle, largely solving the common problems of high residual lithium, poor rate and cycle performance of high-nickel cathode materials in the industry. In Comparative Example 1, lithium sulfate was not used for intercalation and pore formation, resulting in a lower porosity, and the overall capacity, rate and cycle performance were poor; in Comparative Example 2, the addition amount of the intercalation additive substance was small, resulting in a smaller porosity, and the capacity, rate and cycle performance were also poor overall; in Comparative Example 3 during the water washing process, the solid-liquid mass ratio was large, and the intercalated substances were not fully removed and remained in the gaps between primary particles in large amounts, resulting in a smaller porosity and poor overall capacity, rate and cycle performance. It can be seen that the materials in Comparative Examples 1-3 have a relatively low overall porosity, a longer lithium-ion transmission distance, a relatively large polarization internal resistance, and poor capacity, rate and cycle performance, and the overall electrochemical performance is poor compared with the examples.

[0087] In summary, the present invention modifies the matrix structure and morphology of the nickel-based cathode material by using high electronegativity and high solubility inorganic acid salts doping combined with a water washing process to achieve intercalation and pore formation modification, forming a material with low residual lithium, high porosity and high stability, shortening the diffusion distance of lithium ions, increasing the diffusion speed of lithium ions, eliminating grain boundary stress at the same time, reducing lithium-nickel mixing, exhibiting a higher capacity, having better rate performance, doping with high electronegativity elements to stabilize lattice oxygen, reducing oxygen loss, having a higher oxidation potential, thereby improving the structural stability of the material. At the same time, the coating process is combined to repair the surface structure defects generated during the water washing process, reduce the surface stress of the material, form an ionic conductor layer, protect the surface of the material, reduce the side reactions with the electrolyte during the cycle, improve the cycle stability of the material, and achieve high capacity, high rate and long cycle performance, meeting the requirements of EV long-endurance vehicle battery materials.

Claims

1. A modified nickel-based cathode material, comprising a nickel-based cathode material matrix and a doping element doped in the nickel-based cathode material matrix, characterized in that, The doping element includes a doping element L with high electronegativity, and the electronegativity of the doping element L is higher than that of lithium and transition metal elements in the nickel-based cathode material matrix. The porosity of the modified nickel-based cathode material is 10%-20%.

2. The modified nickel-based cathode material according to claim 1, wherein The electronegativity value of the doping element L > 2.

0.

3. The modified nickel-based cathode material according to claim 2, characterized in that, The doping element L includes at least one of B, C, N, S, F, Cl, Br, or I.

4. The modified nickel-based cathode material according to claim 1, wherein The mass of the doping element L accounts for 0.05%-0.2% of the total mass of the modified nickel-based cathode material.

5. The modified nickel-based cathode material according to claim 1, wherein The specific surface area of the modified nickel-based cathode material is 0.8 - 1.5 m 2 / g, and the total residual lithium on its surface is 1000 - 1800 ppm.

6. The modified nickel-based cathode material according to any one of claims 1 to 5, characterized in that, The chemical general formula of the modified nickel-based cathode material is Li z Ni 1-x-y Co x Me y L u M v N w O 2-t , where 0.9 ≤ z ≤ 1.1, 0 ≤ x ≤ 0.2, 0 ≤ y ≤ 0.2, 0 < u ≤ 0.007, 0 ≤ v ≤ 0.01, 0 ≤ w ≤ 0.01, -0.05 ≤ t ≤ 0.05, Me is at least one of Mn and Al, M is at least one of Na, K, Mg, Ca, Sr, Ba, Zr, Ti, and Y, and N is at least one of B, La, Ce, Al, Co, Ti, or W.

7. A method for preparing a modified nickel-based cathode material according to any one of claims 1 to 6, characterized in that, It includes the following steps: (1) Mix the cathode material precursor, lithium source, and dopant evenly and then perform sintering treatment to obtain a sintered product; (2) Wash the sintered product obtained in step (1) with water and dry it to obtain a washed product; (3) Mix the washed product obtained in step (2) evenly with a coating agent containing element N, and then perform sintering treatment to obtain a modified nickel-based cathode material.

8. The preparation method according to claim 7, characterized in that, In step (1), the dopant includes a dopant containing element L, and the mass ratio of its addition amount to the cathode material precursor is denoted as a, and a is 2% to 8%; the dopant containing element L is an inorganic acid salt, and its solubility s at 20°C is greater than 10 g / 100 g of water.

9. The preparation method according to claim 8, characterized in that, In step (2), during the water washing process, the solid-liquid mass ratio is denoted as b, and b ≤ s(1 + a) / 500a.

10. The preparation method according to claim 9, characterized in that, In step (2), during the water washing process, the solid-liquid mass ratio b is 0.5-1.8, the water washing temperature is 5-25°C, and the stirring speed is 500-900 rpm.

11. The preparation method according to claim 7, characterized in that, In step (1), the sintering treatment includes two-stage sintering. First, heat up to 400-600°C for the first-stage sintering, and the holding time for the first-stage sintering is 2-5 h. Then, heat up to 700-900°C for the second-stage sintering, and the holding time for the second-stage sintering is 8-20 h.

12. The preparation method according to claim 7, characterized in that, In step (3), the temperature of the sintering treatment is 300-700°C, and the holding time for sintering is 4-10 h.

13. A lithium-ion battery, characterized in that, The cathode material used in the lithium-ion battery is the modified nickel-based cathode material described in any one of claims 1 to 6 or the modified nickel-based cathode material prepared by the preparation method described in any one of claims 7 to 12.

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